//http://jsfiddle.net/Lqcde/3/

//html
<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>
<div id="map_canvas"></div>
//css
html, body, #map_canvas { margin: 0; padding: 0; height: 100% }

//javascript
var location1 = new google.maps.LatLng(34.04429454929703, -118.22793351693724);
var location2 = new google.maps.LatLng(33.688522885631706, -116.15151750131224);

var location3 = new google.maps.LatLng(32.69561555501597, -117.06338273568724);
var location4 = new google.maps.LatLng(34.525395303965354, -117.27212297006224);

var map;
var mapOptions = { center: new google.maps.LatLng(42.5584308, -70.8597732), zoom: 3,
  mapTypeId: google.maps.MapTypeId.ROADMAP };

function initialize() {
  map = new google.maps.Map(document.getElementById("map_canvas"), mapOptions);
  directionsService = new google.maps.DirectionsService();
  directionsDisplay = new google.maps.DirectionsRenderer({
    suppressMarkers: false,
    suppressInfoWindows: true
  });
  directionsDisplay.setMap(map);

  var request = {
    origin: location1, 
    destination: location2,
    travelMode: google.maps.DirectionsTravelMode.DRIVING
  };
  directionsService.route(request, function(response, status) {
    if (status == google.maps.DirectionsStatus.OK) {
      directionsDisplay.setDirections(response);
    }
  });


  //directionsService = new google.maps.DirectionsService();
  directionsDisplay2 = new google.maps.DirectionsRenderer({
    suppressMarkers: false,
    suppressInfoWindows: true
  });
  directionsDisplay2.setMap(map);

  var request = {
    origin: location3, 
    destination: location4,
    travelMode: google.maps.DirectionsTravelMode.DRIVING
  };
  directionsService.route(request, function(response, status) {
    if (status == google.maps.DirectionsStatus.OK) {
      directionsDisplay2.setDirections(response);
    }
  });
}
google.maps.event.addDomListener(window, 'load', initialize);